In the integrated circuit (IC) industry, semiconductor wafers are measured electrically and/or optically during research, during manufacturing, or after manufacturing to determine various characteristics of either regions or devices on the wafer. Typically, these measurements are made by placing the semiconductor wafer onto a wafer chuck. This wafer chuck is then moved in a three-dimentional manner which requires X axis control, Y axis control, and Z axis control. In order to get accurate results, many X-Y points on the surface of the wafer are measured. Each X-Y location on the wafer requires a change in the X direction and Y direction.
As semiconductor wafers increase in diameter, the use of an X-Y coordinate system to perform these metrology measurements on a semiconductor wafer becomes inefficient. First, the alignment and control required for an X-Y system are sophisticated and are therefore very costly to implement. In addition, the X-Y system requires more fine alignment and control thereby reducing the throughput of a metrology tool. In addition, X and Y motion control results in a significant amount of motion per wafer location. This additional motion may increase maintenance costs or reduce the life of the apparatus as well as reducing the amount of time that the system is actually performing useful work. As wafer sizes increase and the number of measurements per wafer increase, the costs and throughput loss will become even more significant.
Therefore, the need exists for a new metrology methodology which can more efficiently measure larger diameter semiconductor wafers that require many measurement points.